IL-23 belongs to the IL-12-family and as such is a heterodimeric cytokine. It is composed of a p40-subunit—shared with IL-12, where it binds to a p35 entity—and a p19-subunit linked by a disulfide bond (Oppmann et al., 2000). When first discovered, the p19 subunit was designated IL-B30. It was soon discovered that this subunit displays biological functions only when paired with the p40 subunit (Oppmann et al., 2000).
Several functional domains have been described in the subunits: A domain forming the interaction-surface of p19 with its receptor IL23R, a domain forming the interaction surface of p40 with a part of the IL-12 receptor, IL12Rβ1, a domain for the interaction of p40 with IL23R and domains on both p19 and p40, facilitating interaction of the two subunits.
The receptor conferring specificity for IL-23 is a member of the hemopoietin receptor family and is paired with IL-12Rβ1, the receptor binding IL12p40. When bound by its ligand, the receptor signals through the JAK/STAT-pathway, involving predominantly STAT3, but also STAT1, STAT4, and STAT5.
Functionally, IL-23 is involved in the induction of proliferation of memory T cells (Oppmann et al., 2000) and is unique in the generation, stabilization and maintainance of Th17 cells from naïve T cells. Th17 cells are a recently described line of T cell differentiation apart from Th1 and Th2 cells, and express a large number of cytokines and proinflammatory effectors. Furthermore, IL-23 plays a role in the biology of various Type 17 immune cells, a polymorphous group of cell populations with mostly yet unclear properties and roles (Gaffen et al., 2014).
Tests for IL-23-function are sparse. The standard assay today is a cellular assay, which quantifies the ability of isolated murine splenocytes to produce IL-17A after stimulation with human IL-23 (Aggarwal et al., 2003). This assay is routinely used by manufacturers of rIL-23 to assess the quality of their products. A molecular assay, termed “STAT3-Assay” capitalizes on the fact that STAT3 is phosphorylated at Y705 following binding of IL-23 to its receptor and signalling through JAK2 and TYK2. Phosphorylation of STAT3 can be monitored with STAT3p-specific monoclonal antibodies in flow cytometry. Other assays based on colorimetric reactions after IL-23-induced cell growth of different cell lines have been reported in the literature but failed to be reproducible in our hands.
IL-23 has been shown to be significantly involved in several malignancies. Most prominent among these and best researched in this context stands psoriasis.
Psoriasis is a chronic and recurrent inflammatory dermatosis that can be triggered by exogenous and endogenous noxes (reviewed in (Wippel-Slupetzky and Stingl, 2009)). The disease affects approximately 2% of the population and is associated to a decreased quality of life (discomfort, disability, curtailed social interaction, comorbidities). As the disease is still incurable, treatment-intensive and a massive strain to patients in physic, psychic, social and material aspects, which can amount to suicidal tendencies, there is an ample need for novel and effective therapies. The yearly market for psoriasis-related therapies is estimated at 3.3 billion USD/year.
The etiology of the disease remains unresolved, numerous possible endo- and exogenous triggers concur with a genetic predisposition, the inheritance patterns for susceptibility to psoriasis being complex. Recent data show that IL-23 plays a central role in the development and perpetuation of the disease. Both the cytokine and its receptor are genetically associated to the malady, and the cytokines' expression is clearly increased in psoriatic lesions as compared to normal skin (Lee et al., 2004).
IL-23, a large proportion of which is produced by monocytes and dendritic cells—probably triggered by products of damaged keratinocytes—contributes to inflammation by stimulating and maintaining Th17 cells, which in turn express several cytokines, among them IL-17A that activates production of various inflammatory effectors and chemokines and thus contributes to the creation of an inflammatory environment, and IL-22, which triggers hyperproliferation of keratinocytes. The damaged keratinocytes in turn attract chemotactically more cells of the immune system, causing aggravation of the inflammation (Nestle et al., 2009).
Besides psoriasis, several other diseases have been linked to a deregulation of the Th17/IL-23 pathway (reviewed e.g. in (Gaffen et al., 2014)), e.g.: Rheumatoid arthritis, systemic lupus erythematosus, Diabetes, Atherosclerosis, inflammatory bowel disease/M. Crohn, multiple sclerosis, Behçet disease, ankylosing spondylitis, Vogt-Koyanagi-Harada disease, chronic granulomatous disease, hidratenitis suppurtiva, ANCA-associated vasculitides and M. Alzheimer, as well as various forms of cancer. The list is growing at a fast pace.
Novel antibody-based therapies aim at a reduction of IL-23 in patients with psoriasis. Clinical studies demonstrate that repeated application of antibodies that interfere with the binding of IL-23 to its receptors lead to a significant and enduring improvement of the diseases' symptoms (Cingoz, 2009). As a consequence of these studies, one antibody (Ustekinumab/Stelara®) has been approved for the treatment of psoriasis, while several others are in development. Vaccination of mice with certain KLH-coupled peptides derived from the murine IL-23 subunit-sequences has been demonstrated to be effective against arthritis and IBD.
WO 2005/108425 A1 relates to the IL-23p19 antigen in array form. The article of Ratsimandresy et al. (Vaccine 29 (2011): 9329-9336) reports an active immunization against IL-23p19 using specific peptides. The article of Guan et al. (Immunotherapy 5 (2013): 1313-1322) discloses an IL-23p19 vaccine to block IL-23 ameliorating chronic murine colitis. WO 2007/027714 A2 discloses engineeres anti-IL-23-antibodies.